> Why is there more to suspend to RAM than just turning every piece of
> hardware that you know that you reliably can to the lowest power setting
> that you know how to
And that is how things are done in ARM land. Some machines go even further
and power on hardware only when they are under use, rather than only
powering them down on explicit "suspend" event.
> and if there is too much hardware that you don't know you can reliably
> suspend, just failing? Or is it religious reasons of wanting to use BIOS
> ACPI code at all costs?
Using VGA bios for display adapters was kinda mandatory before Kernel
Modesetting. I believe on X86 it is kinda tricky to suspend some devices
using ACPI BIOS and others from kernel drivers. To efficiently use driver-
based suspend the ACPI usage should be stopped completely.